Builder's spirit levels have been in wide use for decades, perhaps centuries, for establishing reference lines and planes used during construction of roads, buildings, sidewalks and the like. A more recent innovation is a builder's level which includes spirit vials for levelling and which also includes a laser light source for "spotting" a remote reference point upon a structure.
Equally common are the tripods upon which such levels are supported and examples of earlier tripods and levels are disclosed in U.S. Pat. No. 494,876 (Merrill), U.S. Pat. No. 753,149 (Lankford), U.S. Pat. No. 1,151,549 (Schade) and U.S. Pat. No. 2,308,206 (Poland). One of the features of the tripods shown in the Lankford and Schade patents is a levelling screw arrangement.
More recently developed tripods used by professional engineers and builders have a number of additional features not disclosed in the Merrill, Lankford, Schade and Poland patents. And while such features make the tripod easier to use and more accurate in use, the cost of such professional tripods has risen accordingly. In a modern, professional tripod, the levelling screw platform and related hardware is, itself, a rather costly component of the tripod.
A professional engineer or builder can justify the expense of such a tripod--after all, the tripod is an important tool of the profession and is subjected to use, perhaps hard use, daily or nearly so. But a homeowner/builder who might use a tripod only infrequently to, e.g., lay a sidewalk, build a shed or the like, has great difficulty justifying the expense of a professional-class tripod.
And that is not the only reason why a professional-class tripod might not be appropriate for the casual user. Another reason relates to ease (or, conversely, complexity) of operation. Modern professional-class tripods have a number of parts, including adjustment-related parts which, while contributing to the absolute accuracy required by a professional, may be baffling to the uninitiated user.
In view of the invention, it is neither necessary nor desirable for the casual homeowner/builder to employ a professional-quality tripod or, for that matter, to employ any tripod at all.